Air oil cooler airflow augmentation system

ABSTRACT

An oil supply system for a gas turbine engine has a lubricant pump delivering lubricant to an outlet line. The outlet line is split into at least a hot line and into a cool line, with the hot line directed primarily to locations associated with an engine that are not intended to receive cooler lubricant, and the cool line directed through one or more heat exchangers at which lubricant is cooled. The cool line then is routed to a fan drive gear system of an associated gas turbine engine. A method and apparatus are disclosed. The heat exchangers include at least an air/oil cooler wherein air is pulled across the air/oil cooler to cool oil. The air/oil cooler is provided with an ejector tapping compressed air from a compressor section to increase airflow across the air/oil cooler.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/774,412, filed on Sep. 10, 2015, which is a National Stage Entry ofPCT Application No. PCT/US2014/027652, filed on Mar. 14, 2014, whichclaims priority to U.S. Provisional Application No. 61/787,161 filed onMar. 15, 2013.

BACKGROUND

This application relates to an oil system for providing oil to a gearassociated with a geared turbofan in a gas turbine engine.

Gas turbine engines are known, and typically include a fan deliveringair into a compressor section. Compressed air from the compressorsection is delivered into a combustion section, mixed with fuel, andignited. Products of this combustion pass downstream over turbine rotorswhich are driven to rotate.

A low pressure turbine rotor drives a low pressure compressor, andtraditionally has driven a fan at the same rate of speed. More recently,a gear reduction has been included between the low pressure turbine andthe fan such that the fan and the low pressure compressor can rotate atdifferent speeds. Oil management systems typically provide oil to enginebearings and other locations within the engine. As a result of gearsbeing added to turbofan engines, additional components require cooling,thereby necessitating new cooling systems and methodologies. Heatexchangers are utilized in such systems to maintain lubricant withindesired thermal limits.

A heat exchanger may be utilized airflow to cool the lubricant. The heatexchanger is sized based on the available airflow during all operationalconditions. Air flow available for cooling at low power staticconditions may not be as much as is available during higher power flightconditions. The heat exchanger is necessarily increased in size tocompensate for the lower airflow while maintaining the desired heatexchange capabilities.

Large heat exchanges provided based on lower power and operationinflicts a weight penalty that can reduce the efficiencies provided bythe gear reduction. Accordingly, it is desirable to design and developdevise that provide the heat exchange capability while improving engineoperating efficiency.

These and other features disclosed herein can be best understood fromthe following specification and drawings, the following of which is abrief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an embodiment of a gas turbine engine.

FIG. 2 is a schematic of an embodiment of an oil management system forthe gas turbine engine of FIG. 1.

FIG. 3 shows an embodiment of an air/oil cooler used in the oilmanagement system of FIG. 2.

FIG. 4 is a schematic view of duct for an air/oil cooler including anejector.

FIG. 5 is a perspective view of an example ejector of the air/oilcooler.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmenter section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flowpath B whilethe compressor section 24 drives air along a core flowpath C forcompression and communication into the combustor section 26 thenexpansion through the turbine section 28. Although depicted as aturbofan gas turbine engine in the disclosed non-limiting embodiment, itshould be understood that the concepts described herein are not limitedto use with turbofans as the teachings may be applied to other types ofturbine engines including three-spool architectures.

The engine 20 generally includes a low speed spool 30 and a high speedspool 32 mounted for rotation about an engine central longitudinal axisA relative to an engine static structure 36 via several bearing systems38. It should be understood that various bearing systems 38 at variouslocations may alternatively or additionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a low pressure compressor 44 and a low pressureturbine 46. The inner shaft 40 is connected to the fan 42 through ageared architecture 48 (shown schematically) to drive the fan 42 at alower speed than the low speed spool 30. The high speed spool 32includes an outer shaft 50 that interconnects a high pressure compressor52 and high pressure turbine 54. A combustor 56 is arranged between thehigh pressure compressor 52 and the high pressure turbine 54. Amid-turbine frame 57 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 57 further supports bearing systems 38in the turbine section 28. The inner shaft 40 and the outer shaft 50 areconcentric and rotate via bearing systems 38 about the engine centrallongitudinal axis A which is collinear with their longitudinal axes.

The core airflow C is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path. The turbines 46, 54 rotationally drive therespective low speed spool 30 and high speed spool 32 in response to thepreviously mentioned expansion.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than ten (10), the gearedarchitecture 48 is an epicyclic gear train, such as a planetary gearsystem or other gear system, with a gear reduction ratio of greater thanabout 2.3 and the low pressure turbine 46 has a pressure ratio that isgreater than about 5. In one disclosed embodiment, the engine 20 bypassratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout 5:1. Low pressure turbine 46 pressure ratio is pressure measuredprior to inlet of low pressure turbine 46 as related to the pressure atthe outlet of the low pressure turbine 46 prior to an exhaust nozzle.The geared architecture 48 may be an epicycle gear train, such as aplanetary gear system or other gear system, with a gear reduction ratioof greater than about 2.5:1. It should be understood, however, that theabove parameters are only exemplary of one embodiment of a gearedarchitecture engine and that the present invention is applicable toother gas turbine engines including direct drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as bucket cruiseThrust Specific Fuel Consumption (“TSFC”). TSFC is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tambient degR)/518.7)∧0.5]. The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 illustrates an oil management system for the gas turbine enginesystem of FIG. 1. The oil management system 140 is utilized inassociation with a fuel system 143, and an integrated drive generator(“IDG”) 160 and its oil cooling system circuit 162.

Fuel from a fuel tank 142 passes to a fuel/oil cooler 144. The fuel isheated, and cools a lubricant, as will be explained below. A main fuelpump 146 drives the fuel into further fuel lines 243 and then into afuel management unit (“FMU”) 148 associated with a combustor, such ascombustor 26 as shown in FIG. 1. It is known in the art to heat the fuelto improve the efficiency of the overall engine. The fuel/oil cooler 144provides this function.

At the same time, the IDG 160 is driven by turbine rotors to generateelectricity for various uses on an aircraft. As shown in oil coolingsystem circuit 162, the oil from IDG 160 passes through an oil-to-oilcooler 164, and may also thereafter pass through a fuel oil cooler 19before returning to the variable frequency generator 160.

A boost pump 17 may drive the fuel from the tank 142 through the fueloil cooler 19 to heat the fuel, and cool the oil being returned to thegenerator 160. A valve 18 may selectively return fuel to the fuel tank142. As also shown, a bypass directional control valve 16 selectivelybypasses fuel away from the FMU 148 to either upstream or downstream ofthe engine FOC (144). The main fuel pump 146 may be a fixed displacementpump, and thus is less able to provide precise metering of the fuelbeing delivered to the FMU. The bypass valve 16 assists in ensuring theproper amount of fuel is delivered. As shown, the fuel may be returnedthrough a line 15 to a location upstream of the fuel oil cooler 144under certain conditions, low power for example. On the other hand,under other conditions, such as high power, the fuel is deliveredthrough a line 14 to a location downstream of the fuel oil cooler. Sincethe fuel in either line 14 or 15 has already been heated, it may benecessary to provide more cooling to the oil, and thus an improvedair/oil cooler 68 is utilized, and will be explained below.

An oil supply system 150 includes a main oil pump 70 taking oil from amain oil tank 72. The terms “oil” and “lubricant” are usedinterchangeably in this application and cover a fluid used to lubricatesurfaces subject to relative rotation. The oil is delivered through adownstream line 73, and split between two lines 74 and 75. Line 74 issent directly to line 86 without cooling. A modulating valve 76 iscontrolled to achieve a desired fuel temperature for the oil in line 75.As an example, a sensor 300 may send a signal to a control regarding asensed temperature of the fuel downstream of the fuel oil cooler 144.The valve 76 routes the volume of oil between line 78 and 80 to achievethe desired temperature of the fuel.

The oil passing to line 78 passes through the fuel/oil cooler 144 andheats the fuel. The oil is cooled before returning to a commondownstream line 82. The downstream line 82 could be called a “cool” oilline, as the oil will be cooler than the oil in “hot” line 74 which hasnot been cooled in any heat exchanger. For purposes of this application,line 75 is seen as part of the “cool” line even though the lubricant hasyet to be cooled.

The oil directed by the valve 76 into line 80 passes through anair-to-oil cooler at 68 which is exposed to air which is cooler than theoil in line 80, and which cools the oil. Downstream of the air-to-oilcooler 68, the oil passes through the oil-to-oil cooler 164, and mayactually be somewhat heated by cooling the oil for the IDG. Still, theoil reaching line 82 downstream of the oil-to-oil cooler 164 will besignificantly cooler than the oil in line 74. Some of the oil in line 82is directed through a line 84, to a bearing 152, which is part of thegear reduction 48 (see FIG. 1). Thus, cooler oil is supplied to thebearing 152 than is supplied from the line 74. As can be seen, a line 86branches off of the “cool” line 82 at or near the point at which “cool”line 84 breaks away to go to the bearing 152. The lubricant in line 86mixes with the lubricant in “hot” line 74, but downstream of the branchline 84. As shown, the fan drive gears 154 receive “hot” oil. On theother hand, the fan drive gears 154 may be placed to receive the cooleroil. The bearing 152 may include a bearing assembly for supportingrotation of a gear. The bearing assembly may include roller bearingssuch as ball, cylinder or any other roller bearing configuration thatsupports rotation. The bearing 152 may also be configured as a journalbearing.

It is desirable to provide cooler oil to these locations than isnecessary to be supplied to bearings 90, or other locations associatedwith the engine. The bearings 90 as shown in FIG. 2 may equate to theseveral locations of bearings 38 as shown in FIG. 1.

On the other hand, cooling all of the oil associated with the enginebearings 90 would reduce the overall efficiency of the engine. Thus,splitting the oil, and cooling the oil to be directed to the bearing 152provides cooler oil to those locations, while still allowing the hotteroil to be directed to locations that do not need cooler oil.

In addition, a valve 92 can selectively direct additional oil to thegears 154 if additional oil is necessary, such as at high power times.At other times, the valve 92 may direct lubricant through line 94 backto a return line 95 leading back to the oil tank 72.

The overall configuration thus results in an oil supply system whichdirects hotter oil to the locations which do not need cooler oil, butwhich also cools oil to be directed to areas associated with the fandrive gear.

Further details of a similar oil management system are disclosed inco-pending U.S. patent application Ser. No. 13/361,997, entitled “GasTurbine Engine With Geared Turbofan and Oil Thermal Management System,filed on even date herewith, and owned by the assignee of the presentapplication.

The differences between the present application and the above referencedapplication largely relate to the inclusion in the system of the bypassvalve 16. Since fuel which has already been heated is returned by thebypass valve 16, there is more of a cooling load on the oil in theengine fuel oil cooler. Since the bypass valve 16 is returning fuelwhich has already been heated to locations upstream of the FMU, andtemperature sensor 300, it is possible that less heating of the fuel,and subsequently less cooling of the oil will occur in the fuel oilcooler. Thus, the cooling load on the air/oil cooler 68 may be higher.For that reason, an ejector 198 is included, and a tap to a compressorsource 200 (e.g., the sixth stage of the compressor section, forexample, such as shown in FIG. 1) may tap high pressure air through theejector 198 to draw additional air into a duct 199, shown schematically,and across the air/oil cooler 68. This will increase the amount ofcooling of the oil in the air/oil cooler 68, and ensure the oil reachingline 82 is sufficiently cool to be sent to the bearing 152.

The use of the fuel oil cooler 19 also heats the fuel, and thus reducesthe potential for adequately cooling the oil in the fuel/oil cooler 144on its own. This again points to the use of the improved air/oil cooler.

FIG. 3 schematically shows further details of the air/oil cooler 68. Asshown, a duct 199 bleeds air across the air/oil cooler 68. An ejectortap 198 from a source of compressed air 200 increases the flow of air toachieve adequate cooling of the oil. A valve 201 selectively controlsthis ejector flow.

The air/oil cooler is not in series with the fuel/oil cooler, however byfurther cooling the oil, when it is intermixed, it will be able tocompensate for the hotter oil from the fuel/oil cooler 144.

Referring to FIGS. 4 and 5, an example ejector 224 is supported withinan exit duct 215 downstream from an air/oil heat exchanger 218. An inletduct 212 receives inlet air 214 from a fairing 210. The fairing 210 isdisposed within a bypass flow path B and directs the inlet air 214 intothe inlet duct 212 and through the heat exchanger 218. It should beunderstood that although the example heat exchanger 218 is an air to oilheat exchanger, other configurations of heat exchangers that utilizedairflow are within the contemplation of this disclosure.

The heat exchanger 218 receives in inlet oil flow 220 of hot oil that isthen cooled and generates an outlet oil flow 222 that is cooler than theinlet oil flow 220. The ejector 224 includes a plurality of nozzles 238that generate a high speed ejector airflow 234 that increases airflowthrough the exit duct 215 to increase cooling airflow through the heatexchanger 218.

Due to the lower fan pressure ratios provided in the example gearedturbofan engine 20, adequate airflow through the heat exchanger 218 maynot be available at low power, static conditions such as idling on theground. A heat exchanger sized to provide adequate cooling at low powerstatic conditions would be unnecessarily large for all other engineoperating conditions. Accordingly, the example ejector 224 is suppliedwith compressed airflow to augment airflow through the heat exchanger218.

Compressed airflow 222 is provided by a compressed air source. In oneexample, the compressed air is from a compressor section schematicallyindicated at 226. Compressed airflow 222 may also be provided by a fan228. The fan 228 may be selectively actuated to provide augmentedairflow 222 when required in low power static conditions. The fan 228can be powered by an electric motor 230. The fan 228 may also be poweredthrough a mechanical linkage 232 such as from a power take off shaftdriven by a shaft of the engine 20.

The nozzles 238 are feed compressed airflow through manifold 236. Eachof the nozzles 238 include shrouds 240 to reduce pressure losses withinthe duct. The nozzles 238 utilize the high pressure airflow 22 and ejecthigh velocity airflow 234 from the ejector nozzles 238. The highvelocity airflow 234 entrains additional cool air flow through the heatexchanger 218. The additional airflow provided through the ejector 224enables a smaller more compact heat exchanger 218 to be utilized withaugmented airflow during low power static conditions. During higherpower operating conditions, the augmented airflow is not required asairflow drawn in through the fairing 210 provides sufficient coolingperformance for the heat exchanger 218.

Accordingly, rather than utilizing a large heat exchanger suitable forlow power static conditions for ground idle heat loads, a heat exchangersuitable for use during higher power conditions can be utilized with theaddition of the selectively engageable ejector 224. Smaller heatexchanges can therefore be utilized to provide cooling requirements inall operational conditions.

Although an embodiment of this disclosure has been explained, a workerof ordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

The invention claimed is:
 1. A lubricant supply system for a gas turbineengine comprising: a lubricant pump delivering lubricant to an outletline that splits into at least a hot line and a cool line, said hot linebeing directed primarily to locations associated with the gas turbineengine that are not intended to receive cooler lubricant, and said coolline being directed to at least one component with an operatingtemperature lower than the locations associated with the gas turbineengine that are not intended to receive cooler lubricant; an air/oilcooler that pulls air across said air/oil cooler to cool lubricant insaid cool line, wherein at least a portion of the lubricant in said coolline bypasses the air/oil cooler and is passed through a first fuel/oilcooler configured to cool the at least a portion of the lubricant usingfuel leading to a combustion section of the gas turbine engine; anoil/oil cooler configured to cool lubricant from a generator withlubricant from the air/oil cooler; and a second fuel/oil coolerconfigured to cool another lubricant exhausted from the oil/oil coolerwith the fuel leading to the combustion section.
 2. The system asrecited in claim 1, including an ejector within the air/oil cooler foraugmenting air flow across the air/oil cooler selectively responsive toan operating condition not providing air flow sufficient for coolinglubricant to desired temperature.
 3. The system as recited in claim 2,including selectively actuating a fan to provide airflow through to theejector to augment airflow across the air/oil cooler.
 4. The system asrecited in claim 2, including selectively providing airflow from acompressor section to provide airflow to the ejector to augment airflowacross the air/oil cooler.
 5. The system as set forth in claim 1,wherein a valve is positioned on said cool line and splits said coolline into two lines, with a first line being directed through said firstfuel/oil cooler at which the at least a portion of the lubricant iscooled by fuel leading to the combustion section of the gas turbineengine, and the lubricant in the cool line that is not being directed tothe first fuel/oil cooler is directed through a second line, said coolline being split into said two lines at a location downstream of a pointwhere said outlet line is split into said hot line and said cool line.6. The system as set forth in claim 5, wherein a bypass valveselectively bypasses fuel downstream of said fuel/oil cooler backupstream.
 7. The system as set forth in claim 6, wherein said bypassvalve alternatively directs the fuel upstream of the first fuel/oilcooler, or downstream of the first fuel/oil cooler.
 8. The system as setforth in claim 1, wherein the second fuel/oil cooler is at a locationupstream of said first fuel/oil cooler.
 9. A gas turbine enginecomprising: a fan, a compressor section, including a low pressurecompressor section and a high pressure compressor section; a combustor;a turbine section including both a low pressure turbine and a highpressure turbine section, and said low pressure turbine section drivingsaid low pressure compressor section; and a fan drive gear systemprovided such that said low pressure turbine further driving said fan,with said fan and said low pressure compressor being driven at differentspeeds; a lubricant system including a lubricant pump deliveringlubricant to an outlet line that splits into at least a hot line and acool line, said hot line being directed primarily to locationsassociated with the gas turbine engine that are not intended to receivecooler lubricant, and said cool line being directed to at least onecomponent with an operating temperature lower than the locationsassociated with the gas turbine engine that are not intended to receivecooler lubricant; and an air/oil cooler wherein air is pulled acrosssaid air/oil cooler to cool lubricant in said cool line, wherein atleast a portion of the lubricant in said cool line bypasses the air/oilcooler and is passed through a first fuel/oil cooler configured to coolthe at least a portion of the lubricant using fuel leading to acombustion section of the associated gas turbine engine; an oil/oilcooler configured to cool lubricant from a generator with lubricant fromthe air/oil cooler; and a second fuel/oil cooler configured to coolanother lubricant exhausted from the oil/oil cooler with the fuelleading to the combustion section.
 10. The gas turbine engine as recitedin claim 9, including an ejector within the air/oil cooler foraugmenting air flow across the air/oil cooler selectively responsive toan operating condition not providing air flow sufficient for coolinglubricant to desired temperature.
 11. The gas turbine engine as recitedin claim 10, including selectively actuating a fan to provide airflowthrough to the ejector to augment airflow across the air/oil cooler. 12.The gas turbine engine as recited in claim 10, including selectivelyproviding airflow from a compressor section to provide airflow to theejector to augment airflow across the air/oil cooler.
 13. The gasturbine engine as set forth in claim 9, wherein said locations in theengine that are not intended to receive cooler lubricant includebearings associated with at least the turbine section.
 14. The gasturbine engine as recited in claim 9, wherein a valve is positioned onsaid cool line and splits said cool line into two lines, with said firstline being directed through the first fuel/oil cooler at which the atleast a portion of the lubricant is cooled by fuel leading to thecombustion section of the gas turbine engine, and the lubricant in thecool line that is not being directed to the first fuel/oil cooler butbeing directed through a second line and, said cool line is split intosaid two lines at a location downstream of a point where said outletline is split into said hot line and said cool line.
 15. The gas turbineengine as recited in claim 14, wherein a bypass valve selectivelybypasses fuel downstream of said first fuel/oil cooler back upstream.16. The gas turbine engine as recited in claim 15, wherein said bypassvalve alternatively directs the fuel upstream of the first fuel/oilcooler, or downstream of the first fuel/oil cooler.
 17. The gas turbineengine as set forth in claim 15, wherein the second fuel/oil cooler isat a location upstream of said first fuel/oil cooler.
 18. The system asrecited in claim 8, wherein the oil/oil cooler, the generator and thesecond fuel/oil cooler are part of an oil cooling system circuit that isnot in flow communication with lubricant circulated in the at least onehot line and cool line.
 19. The gas turbine engine as recited in claim17, wherein the generator is driven by the turbine section.
 20. The gasturbine engine as recited in claim 17, wherein the oil/oil cooler, thegenerator and the second fuel/oil cooler are part of an oil coolingsystem circuit that is not in flow communication with lubricant in theat least one hot line and cool line.